Alternating-current motor



Aug. 19, 1924. Y, 1,505,619

. S. R. BERGMAN ET AL ALTERNATNG CURRENT Moron Inventors:

Patented Aug. 19, 1924.

UNITED f s-TATES PATENT OFFICE-,5

SVEN E. BERGMAN, or; NAHANT, MASSACHUSETTS, AND ALEEED E. WELCH, or ECET WAYNE, INDIANA, AssreNoEsTo GENERAL ELECTRIC COMPANY, A CoEroEATIoN F NEW YORK.

`.Applicationfiled August y8, 1921. Serial No. 490,482.

To all whom t may concern: e

Be it known that we, SVEN R. BERGMAN, a lsubject of the Kingl of'fSweden, residing atNahant, county of Essex, State of Massachusetts, and ALFRED F. WELCH, a citizen of the United States, residing at Fort Wayne, countyvof Allen, State of Indiana,`have in# vented Acertain ynew and yuseful, Improve` ments in Alternating- Current Motors, of which the following is a specification. y y, This invention relates to an alternating currentA motor, and more particularly toa single phase commutator motor having desirable starting and running Characteristics.

It is `well known that a single phase comrmutator motor whether fed conductivelyor inductively does 'not have a limitedspeed. To limit the speed of such a motor it has beenwproposed to provide `a Squirrel cage winding on the secondary or movablenmember of the commutatormotor. Such a motor has a tendency to run at speed near synchronism and the'` speed 'variation due to Vvariation of loadj is comparatively slight. In the ordinary arrangement of acommutator motor with a squirrelvcage' winding there ishowever objectionably `high starting current as well as low Starting torque. "It, is the main object .of our invention to-make it possibleto starta commutator motor, such for example as a repulsion motor, with a low t starting current and a highv torque. We obtain this effect by a proper construction of the squirrel cage winding on the secondary member of the motor. Thel squirrelvcage winding as used'by us comprises conductors which have a relatively high resistance when starting and a relativelyr low resistance when running. Due to the low'resistance lduring the running conditionthe speed of the motor cannotrise much abovesynchronism. At the same time the reactan'ce of the windings is low during the running condition so that the power factor of the current supplied to the motor is high.` r

For a better understandingk of our invention-reference isto behad to thefollowing description `together with the accompanying drawings, in which Fig. k1 shows the primary and secondary members of the motor built in accordance with our invention with the `conductors making up the windings in cross section;4 Fig. 2 is alongitudinal sectional view of the operating parts of the motor;

i winding 16.

F ig.'3 `is a side view of one of the conductors making up the squirrel cage winding; Fig. L.lis an end view of the same ;v and Fig. 5 is a cross section of a portion ofthe secondary memberk showing a modified form of slots-and conductors used thereon. y

Referring now more in detail to thedr'awf ings, .invwhich like reference characters refer to like parts throughout, the stator or primuy member 11 is Supplied with Siotsie and windings 13. therein. yThe arrangement ofthe windings', as well as the particular vconstruction of they stator member, may be of anywell known form s'incethes'e` constitute C no part of `our invention. Located within the stator 11 and'mounted on the shaft 14 of the motor is the secondary member or 'rotor 15 which isjpreferablymadey upr of laminations appropriately clamped to the H,

shaft 14, as shown iny Fig. `2. lThe Secondary member 15 carries commuted definite coil The `commutator'l? is electricallyv connected .theretov and a pair of brushes 18, if a bi-polar motor is used, is placed upon the commutator 17 andare short circuited in angaxis displaced fromtheaxis of `the windings on the stator or primary member 11. As 4thus far described the motor resembles an ordinary single phase repulsion motor. e l

Located `betweenthe slots. 19 which carry the Vwindings .16 are deep and narrow bars 20. These bars are shown in greater detail in Figs. 3 and 4 and consist of a central member 21 of thin copper and outside members'22of magnetic-material such as Sheet iron.` These three members are preferably welded together and are located in slots 23 appropriately provided on the secondary memberl15. The two outside magnetic members 22. areused merely to illinY the slots whiclrare ditiicult to stamp out ywhen made very narrow. The` active part ofthe `bar Whichis used in the conductor ofthe squirrel ,l f

vcage vwinding is the copper member r21. By

the use of thisexpedientof welding the magnetic members lto ythe copper member it .is possible to utilize slightly wider slots in thejsecondary member so that little diiculty f may be experienced in punching them. The magnetic members 22 thus form a part of ,the "magnetic` `structure of the secondary `member y15. `This form of conductor is shown in a patent granted to Sven R. Bergman, No. 1,240,018, and assigned to the same assignee as the present application. End rings 24 are provided in each end of the squirrel cage for connecting the bars electrically together.

Due to the fact that comparatively deep and narrow bars are utilized in the squirrel cage, when the motor is started the repulsion motor winding 13 predomiiiates, as the squirrel cage winding has a comparatively high apparent resistance. This (pparent resistance is produced by .the ed y currents developed in the bars 21. As the motor continues to speed up the squirrel cage exerts a gradually increasing torque. Near synchronism the resistance of the squirrel cage becomes less since there is no longer an intense magnetic iield 'which sweeps across these conductors. The speed thus rises only slightly above s vnchronisin. Furthermore, during the running operation the squirrel cage has but little `reactance andthe power factor of the motor is maintained at a comparatively high value. During the starting period of the motor the high apparent resistance of the squirrel cage assists materially to produce a .high torque.

In Fig. 5, we show a modified form of the windings of the secondary member 15. In this case the definite coil Winding 25 is located in one part of the slot 26 having a somewhat irregular sha e. The remainder of the slot is occupiedP by the com ound conductor 27 comprising an L-shape copper member 28 and thin stri s of magnetic material 29, 30 and 31. Tiese strips 29, 30 and 31 merely fill in the slot so as to complete the magnetic structure. The active portion ofthe conductor comprises the L- shaped member 2S. This modification operates substantially as the modifications shown in Fig. l, except that the wide portion of the conductor at the bottom of the L is added. This portion rovides a path for the current through tie squirrel cage in iharallel with the path through the deep bar.

iis parallel path, however, during the starting of the motor does not permit a hi current flow, since it is almost entirely ein dded in magnetic material vand its reactance is therefore high. However, near synchronism the reactance is reduced considerably and this parallel path is suiciently good so that it reduces appreciably the total impedance which is opposed to the How of current through the squirrel cage during ruiming operation.

It is evident from the foregoing description that we have produced a single phase self starting motor having desirable starting and running characteristics. These effects are due to the arrangement of the windings of the secondary member and to the form of the conductors making up the squirrel cage winding.

While we have shown in the accompanying dra-wings but several modifications of our invention, we do not wish to` be limited thereto but aim to embrace inthe a pended claims all modifications falling fair y with` in the spirit and scope of our invention.

"hat We claim as new and desiie to secure by Letters Patent of the United States, is:

1 A sin le phase motor comprising a primary meniler and a secondary member, a commutated Winding carried by the secondary member and a squirrel cage winding also carried by the secondary member, the barsl of said squirrel cage vwinding having an enlarged portion situated belowy the commutated winding and a relatively reduced portion extending above said commutated winding.

2. A sin le phase motor comprising a primary mem r and a secondary rotor member, a commutated winding carried by the secondary member and a squirrel cage winding also carried by the secondary member, the 'bars of said squirrel cage winding having-anenlarged ortion situated below the commutated win, ing and a relatively ynarrow portion extending tothe periphery of the rpxtor. l h

' si e-p ase motor com risin a rimary menrber and a secondari; meiibei'), a commutated winding carried by the secondary member, vand a squirrel cage winding also carried the secondary member, said squirrel cage windin hwvin yL-shaA conductors, the vertica arm gf the edbeing radial and comparatively narrow.

4. A sin le phase motor'comprising a primary mem r and a secondary member, a commutated winding carried by the secondary member and a squirrel cage windin alsocarried by the secondary member, said squirrel cage windingbars extending above and' below said commutated winding and ybeing of such form that during the starting period, eddy currents materially increase their apparent resistance.

5. A sm le phase motor comprising a primary mem r and a secondary member, a winding having definite coils carried by said member, and a squirrel cage winding also lcarried by the secondary member, said squirrel cage wind/ing 'hafving L-shaped conductors, the vertical arm of the L being radial and comparatively narrow.

In witness whereof, the said `SVEN R. Braunau has hereunto set his hand this 30th day of July, 1921, and the said Amman F. WEwH has hereunto set his hand this 4th day of Aug., 1921.

.y SVEN R. B'ERGMAN. ALFRED F. WELCH. 

